JPH01176053A - Martensitic stainless steel for cold forging and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a martensitic stainless steel having excellent cold forgeability by extremely reducing the contents of Si and Mn in an SUS 410 type stainless steel and regulating its crystal grain size to the specific value. CONSTITUTION:The SUS 410 type stainless steel material having the compsn. contg., by weight, 0.10-0.16% C, <0.20% Si, <0.25% Mn, <0.005% S and 11.50-12.20% Cr, or furthermore contg. one or more kinds among <1.5% Mo, <0.20% Ti, <0.15% V and <0.10% Nb and the balance consisting of Fe is heated for 2-15hr at 800-950 deg.C to regulate its crystal grain size to the range of 5-8. The martensitic stainless steel material having excellent cold forgeability in such a manner that cracks do not occur at the time of cold forging and furthermore having excellent tensile strength and corrosion resistance can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is used for home appliances, pins and screws for fixing roof panels, and the like. The present invention relates to a high-strength martensitic stainless steel that has excellent cold forgeability in an annealed state, and extremely excellent corrosion resistance and quench hardenability, and a method for producing the same.

[Prior art]

As martensitic stainless steel, generally 5US
Because 410 (0, IC-12, 5Cr) has corrosion resistance and strength, it is widely used in home appliances, pins and screws for fixing roof panels, etc.

[Problems to be solved]

However, the 5US410 has a hardening type of Hv.
427, which is excellent in terms of strength.

Since the tensile strength in the annealed state was as high as 55 kg/+, the cold forgeability was not necessarily satisfactory. There was also a need for improvement in corrosion resistance.

However, in general, when trying to improve cold forgeability, strength decreases; cold forgeability and strength are contradictory characteristics, and it has been difficult to satisfy both.

The present invention aims to address this problem, particularly for Si.

This was achieved after studying the content of Mn and S components and the ferrite crystal grain size, and it shows excellent cold forgeability in the annealed state without reducing the strength in the tempered state, and has excellent corrosion resistance and annealing properties. The purpose is to provide a high-strength martensitic stainless steel with excellent hardening ability.

Solution to Problem C] The present invention is based on three weight ratios of C0.10 to 0.16%, Si
n, 20% or less, Mn 0.25% or less.

s0. The martensitic stainless steel for cold forging is characterized by containing 11.50 to 12.20% of Cr, and the remainder consisting of Fe and impurity elements. (Hereinafter referred to as the first invention steel.

In view of the above-mentioned drawbacks of the above-mentioned 5US410, the present invention provides:
As a result of extensive research into the effects of alloying elements such as C, St, Mn, and Cr on the tensile strength of 2%Cr stainless steel in the annealed state, we found that, first, the strength of the base material is improved by solid solution strengthening. Second, by regulating the grain size to a range of 5 to 8, cold forgeability is improved, and tensile strength is improved with a C content of 0.16% or less. It was discovered that the C content can be reduced to 48 kg f/m or less.
~0.16%, which is the same hardness as conventional steel (Hv400 or higher), and succeeded in lowering the tensile strength in the annealed state by approximately 5 kg f/1m" compared to conventional steel. , which has significantly improved cold forgeability.

That is, the relationship between Si content and tensile strength is as shown in FIG. 1, where the tensile strength increases as the Si content increases. The purpose is to reduce the tensile strength in the annealed state to 48 kgf/8 or less, and the upper limit of the amount of Si is 0.2.
It was set to 0%.

In addition, as shown in Figure 2, the relationship between Mn content and tensile strength is similar to that of St, where the tensile strength increases as the Mn content increases. In the present invention, cold forgeability is improved. The purpose is to obtain a tensile strength of 48 kgf/hofu or less in an annealed state, and the upper limit of the Mn content is set to 0.25%.

Furthermore, as shown in Figure 3, the relationship between grain size and tensile strength is such that as the grain size becomes larger (the grain size becomes smaller), the tensile strength improves.
By doing the following, the tensile strength was lowered to 48 kgf/3 or less. However, if the crystal grain size becomes too coarse, it becomes brittle, easily cracks during cold forging, and causes rough skin, so the crystal grain size is set to 5 or more.

Next, the second invention steel was added to the first invention steel with Mo1.
5% or less, Ti 0.20% or less, VO.

15% or less, Nb 0.10% or less. Due to this.

The tensile strength of the first invention steel in the quenched and tempered state is further improved, and the strength and corrosion resistance during use of the material are further improved.

The reasons for limiting the components in the present invention will be explained below.

C is an element necessary to ensure a quenching hardness of Hv400 or more, and in order to obtain this strength, the lower limit was set to 0°10%.

However, as the amount of C increases, the tensile strength increases and the cold forgeability significantly decreases.

The upper limit was set at 0.16%.

St is an element that is effective in deoxidizing, but it is also a strong ferrite-forming element, and it is also an element that increases strength through solid solution strengthening and reduces cold forgeability, so its content should be minimized. It is necessary to lower the upper limit to 0.20.
%.

Mn is an element that is effective in deoxidizing and is a strong austenite forming element, but on the other hand, it is an element that increases strength through solid solution strengthening and significantly reduces cold forgeability, so its content is Therefore, the upper limit was set at 0.25%.

S is an element that produces MnS, which is the starting point for cracks during cold forging, and significantly reduces cold forging performance, as well as deteriorating corrosion resistance.It is necessary to reduce its content, and the upper limit should be set at 0. It was set as oos%.

In addition, to further improve cold forgeability, add 0.002%.
It is preferable to do the following.

Cr is a basic element that imparts corrosion resistance to stainless steel, and to increase this effect it is necessary to contain it in an amount of 11.50% or more, so the lower limit was set at 11.50%.

On the other hand, Cr is also a strong ferrite-forming element and impairs hardenability, so its upper limit was set at 12.20%.

Next, M0. Ti, V, and Nb are elements that contribute to improving the tensile strength in the tempered state, but on the other hand, they are strong ferrite-forming elements and impair hardenability, so their upper limit is set to M.
o is 0.15%, Ti is 0°20%, ■ is 0.15%,
Nb was set at 0.10%.

Next, as a method for manufacturing the above-mentioned first invention steel.

Weight ratio: C0.10~0.16%, Si0°20%
Below, Mn 0.25% or less, 30.005% or less, Cr
Contains 11.50-12°20%.

Steel consisting of the balance Fe and impurity elements is heated to 800 to 9
There is a method for producing martensitic stainless steel for cold forging, which is characterized by heating at 50°C for 2 to 16 hours and controlling the grain size to 5 to 8 to improve cold forgeability (hereinafter referred to as
(referred to as the third invention).

Further, as a method for manufacturing the above-mentioned second invention steel.

C0. in terms of weight ratio. to ~0.16%, Sin.

20% or less, Mn 0.25% or less, S 0.005% or less, and Crtl 50 to 12.20%.

Furthermore, Mo is 1.5% or less and Ti is 0.20% or less.

A steel containing one or more of V0.15% or less and Nb0.10% or less, with the balance consisting of Fe and impurity elements, is heated at 800 to 950°C for 2 to 16 hours to reduce the grain size to 5. There is a method for producing martensitic stainless steel for cold forging, characterized in that the cold forgeability is improved by controlling the temperature to 8.

However, in the above two methods, the heating temperature was set to 800
~950℃ is because the crystal grain size is 8 below 800℃.
This is because the desired cold forgeability is difficult to obtain. On the other hand, if the temperature exceeds 950°C, the grain size becomes too coarse, which may cause cracking or rough skin during cold forging.

Further, the reason why the heating time is set to 2 to 16 hours is because if it is less than 2 hours, the crystal grain size will not be reduced to 8 or less, making it difficult to obtain the desired cold forgeability. Moreover, if it exceeds 16 hours, the crystal grain size will become too coarse.

There is a risk of cracking and rough skin during cold forging.

[Action and effect]

In the first aspect of the invention, the amount of Si is particularly 0.20% or less.

By setting the Mn content to a low value of 0.25% or less and the S content to a low value of 0.005% or less, the synergistic effect of these and the above-mentioned optimal ranges of C, P, and Cr improves cold forgeability, which is a drawback of conventional steels. This is an improved version of Also.

The grain size of conventional steel was fine (approximately 12),
By considering the heat treatment conditions in relation to the above composition range, the grain size is set to 8 or less, and cold forgeability is improved.

Therefore, according to the first invention, the tensile strength in the annealed state is 48 kg f /ltm" or less, and the cold forgeability can be improved, and also in the quenched and tempered state. Therefore, it can improve the tensile strength and strength of the steel and further improve the corrosion resistance.

The steel of the present invention is a martensitic stainless steel suitable for home appliances, roof plate fixing bottles, screws, etc.

Further, the second invention provides the first invention with M0. T.I., V.

Since one or more types of Nb are contained in a specific amount, not only the same effects as the first invention can be obtained, but also the strength in the -layer quenched and tempered states is further improved.

Further, according to the third invention, the first invention steel having excellent cold forgeability and the like can be manufactured.

Furthermore, according to the fourth invention, the second invention is even more excellent as described above.
Invention steel can be obtained.

〔Example〕

Next, the characteristics of nine inventive steels will be clarified through examples while comparing them with conventional steels and comparative steels.

Table 1 shows the chemical composition of these test steels.

In Table 1, A-L steel is the steel of the present invention.

A to D are the first invention steel, E to the second invention steel, L to P are comparative steels, and Q is the conventional steel 5US410.

Next, Tables 2 and 3 show the test results for the steel samples shown in Table 1.

That is, Table 2 shows that the test steels in Table 1 were held at various temperatures and times, furnace-cooled at a cooling rate of 25°C/Hr to 600°C, and then annealed under the conditions of air cooling. The tensile strength of something.

It shows the aperture and grain size.

Table 3 shows that the temperature was maintained at 1000°C for 1 hour.

The hardness, tensile strength, and corrosion rate of the specimens subjected to oil quenching and those subjected to IHr tempering at 750° C. after the quenching are shown.

Note that the above tensile strength and reduction of area were measured by preparing a JIS No. 4 test piece.

As is clear from Table 2, in the case of annealing at 820°C for 16 hours, the properties after annealing are lower than that of conventional steel 5US.
For 410 steel, the tensile strength is as high as 54 kgf/Kaku 3, and let's compare! IM, N, O both 57-51kgf
It is as high as 1 m-8, and its cold forging properties are poor.

These trends are almost the same in the cases of 860°C x 10 hours and 900°C x 3 hours.

Furthermore, as is clear from Table 3, the comparative steel has a quenched hardness of Hv363. The quenched and tempered hardness is quite low at Hv235, and the corrosion rate of comparative steel P in the quenched and tempered state is as high as 4.1 g/m, Hr.

As mentioned above, both the conventional steel and the comparative steel have some drawbacks in terms of tensile strength, area of area, grain size after annealing, or hardness, tensile strength, and corrosion rate after quenching, quenching and tempering. It can be seen that it has

On the other hand, as is known from Table 2, steel A-, which is the steel of the present invention, has a tensile strength of 46 to 48 kgf/ms and an area of area of 80 to 81 after annealing at 820°C for 16 hours.
%, and the grain size is 6.5-7.6.

The same applies to other annealing states.

Further, the steel of the present invention has a quenching hardness of Hv425 to 469. Hardness after quenching and tempering is Hv241-272, tensile strength is 7
2-81kgf/sho■8, corrosion rate is 2.5-2.9
g/m, low Hr.

As is known from the above, according to the present invention, marten has excellent cold forgeability with a tensile strength of 48 kgfl or less in an annealed state, and excellent tensile strength and corrosion resistance after quenching and tempering. Site-based stainless steel can be obtained.

For comparison, one of the steels of the present invention, N11B.

For C, C and ■ steel, 760℃ x 16 hours or 100℃
After holding at 0"CX for 2 hours, they were cooled and annealed in the same manner as above.Then, these products were measured for the performance shown in Table 4.As a result, the above annealing conditions were 7.
When it is as low as 60℃, the tensile strength is high and the area of area is low.
The grain size has become finer.

Furthermore, in the case of 1000''C, the tensile strength was low, the area of area was high, and the grain size was coarse.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between Si content and tensile strength, Figure 2 is a diagram showing the relationship between Si content and tensile strength.
The figure is a diagram showing the relationship between Mn content and tensile strength, and FIG. 3 is a diagram showing the relationship between crystal grain size and tensile strength. Si (%) MAL (%)

Claims (4)

[Claims] (1) C0.10-0.16% by weight, Si0.
A martensitic stainless steel for cold forging, characterized in that it contains 20% or less, Mn 0.25% or less, S 0.005% or less, Cr 11.50 to 12.20%, and the balance consists of Fe and impurity elements. (2) C0.10-0.16% by weight, Si0.
20% or less, Mn 0.25% or less, S 0.005% or less, Cr 11.50 to 12.20%, and further Mo
Cold forging characterized by containing one or more of 1.5% or less, Ti 0.20% or less, V 0.15% or less, and Nb 0.10% or less, with the remainder consisting of Fe and impurity elements. martensitic stainless steel. (3) C0.10-0.16% by weight, Si0.
A steel containing 20% or less, Mn 0.25% or less, S 0.005% or less, Cr 11.50 to 12.20%, and the balance consisting of Fe and impurity elements is heated at 800 to 950°C for 2
A method for producing martensitic stainless steel for cold forging, characterized in that cold forgeability is improved by heating for ~16 hours and controlling grain size to 5 to 8. (4) C0.10-0.16% by weight, Si0.
20% or less, Mn 0.25% or less, S 0.005% or less, Cr 11.50 to 12.20%, and further Mo
1.5% or less, Ti 0.20% or less, V 0.15% or less, Nb 0.10% or less, and the balance is Fe and impurity elements.
A method for producing martensitic stainless steel for cold forging, characterized in that cold forgeability is improved by heating at ~950°C for 2 to 16 hours and controlling the crystal grain size to 5 to 8.